Optical transmission/reception device, optical communication system, and optical communication method

ABSTRACT

[Problem] To provide an optical transmission/reception device, an optical communication system, an optical communication method, and a program which are capable of securing the confidentiality of information included in an optical signal even when the optical signal is transferred to a device that is not an original transmission destination device. 
     [Solution] This optical transmission/reception device is provided with: a wave separation unit for receiving a wavelength-multiplexed optical signal and separating the same into a plurality of optical signals; a plurality of reception units for receiving each of the plurality of optical signals separated by the wave separation unit; a plurality of output units for outputting optical signals differing in wavelength from each other; a control unit for requesting, in response to the inclusion in the received wavelength-multiplexed optical signal of an optical signal to which a prescribed process has been applied, that a prescribed change be applied to the optical signal outputted by at least one of the plurality of output units; and a wave combining unit for combining the plurality of optical signals outputted from the plurality of output units and outputting the combined signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.15/129,105 filed Sep. 26, 2016, which is a national stage application ofInternational Application No. PCT/JP2015/001579 entitled “OPTICALTRANSMISSION/RECEPTION DEVICE, OPTICAL COMMUNICATION SYSTEM, AND OPTICALCOMMUNICATION METHOD,” filed on Mar. 20, 2015, which claims the benefitof priority of Japanese Patent Application No. 2014-066137, filed onMar. 27, 2014, the disclosures of which are incorporated herein in theirentirety by reference thereto.

TECHNICAL FIELD

The present invention relates to an optical transmission/receptiondevice, an optical communication system, and an optical communicationmethod.

BACKGROUND ART

In recent years, with an increase in traffic, a submarine cable systemis demanded to have a wide-band circuit (line) or to have a networkhaving a high functionality. A technique such as an OADM (OpticalAdd-Drop Multiplexer) or an ROADM (Reconfigurable Optical Add-DropMultiplexer) is therefore applied to a submarine cable system.

A submarine ROADM system uses a wavelength division multiplexing (WDM:Wavelength Division Multiplexing) communication. In a submarine ROADMsystem, for example, a transmit device inputs a client signal as awavelength multiplexed optical signal in a submarine cable toaccommodate a plurality of paths in one optical fiber, thereby improvingflexibility of a network.

In a submarine cable system having an OADM function, the total power ofa signal transmitted in a cable composed of optical fibers is set to beconstant. When a part of wavelength components of a signal disappears bya breakage of the cable or the like, the signal amplifies otherwavelength components, thereby keeping the total power of the signalconstant.

By increasing only the power of a specific wavelength component of asignal up to a predetermined value or larger, however, optical spectrumchanges caused by deterioration of a waveform of the signal or the likeby a nonlinear effect of an optical fiber, thereby deteriorating thetransmission quality of the signal.

An optical communication system described in PTL 1 discloses a techniquein which, when a failure occurs in a cable, the total power of a signalis corrected by a dummy light to secure communication quality. In anoptical communication system described in PTL 1, a terminal equipment(optical transmission device) comprises a dummy light generating unitwhich generates a dummy light corresponding to a location where anoptical signal break has occurred when a cable break failure isgenerated, and keeps the intensity (power) of a signal to be transmittedconstant. PTL 2 describes a configuration for enhancing a securityfunction of a signal wavelength.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No.2010-098547

[PTL 2] Japanese Unexamined Patent Application Publication No.2011-082751

SUMMARY OF INVENTION Technical Problem

As mentioned above, a terminal equipment (optical transmission device)described in PTL 1 needs to generate a dummy light to compensate anoptical signal, and has to comprise a dummy light generating unit.

Accordingly, in order for a terminal equipment (optical transmissiondevice) to compensate an optical signal without comprising a dummy lightgenerating unit, it is considered to compensate a disappeared opticalsignal by an optical signal transmitted by another terminal equipment.When the optical signal transmitted by the other terminal equipment usedfor compensation is received by a device which is not an originalcommunication destination of the optical signal, however, secrecy ofinformation included in the optical signal cannot be secured, which isproblematic.

An object of the present invention is to solve the above-describedproblem, and to provide an optical transmission/reception device, anoptical communication system, an optical communication method, and aprogram in which, even when an optical signal is forwarded to a devicewhich is not an original transmission destination device, secrecy ofinformation included in the optical signal can be secured.

Solution to Problem

An optical transmission/reception device of the present inventioncomprises: a demultiplexing unit which receives a wavelength multiplexedoptical signal, and demultiplexes the signal into a plurality of opticalsignals; a plurality of reception units which receive each of theplurality of optical signals demultiplexed by the demultiplexing unit; aplurality of output units which respectively output optical signalshaving different wavelengths; a control unit which requests to apply apredetermined change to an optical signal output from at least one ofthe plurality of output units, when the received wavelength multiplexedoptical signal includes an optical signal to which a predeterminedprocessing is applied; and a multiplexing unit which multiplexes theplurality of optical signals output from the plurality of output unitsand outputs the multiplexed signal.

An optical communication system of the present invention ischaracterized by comprising: an optical communication device whichoutputs a wavelength multiplexed optical signal; and an opticaltransmission/reception device comprising a demultiplexing unit whichreceives the wavelength multiplexed optical signal, and demultiplexesthe signal into a plurality of optical signals, a plurality of receptionunits which receive each of the plurality of optical signalsdemultiplexed by the demultiplexing unit, a plurality of output unitswhich respectively output optical signals having different wavelengths,a control unit which requests to apply a predetermined change to anoptical signal output from at least one of the plurality of output unitswhen the received wavelength multiplexed optical signal includes anoptical signal to which a predetermined processing is applied, and amultiplexing unit which multiplexes the plurality of optical signalsoutput from the plurality of output units and outputs the multiplexedsignal.

An optical communication method of the present invention ischaracterized by comprising: a multiplexing unit of receiving awavelength multiplexed optical signal; requesting to apply apredetermined change to an optical signal to be output, when thereceived wavelength multiplexed optical signal includes an opticalsignal to which a predetermined processing is applied; and multiplexinga plurality of optical signals having different wavelengths including anoptical signal to which the predetermined change has been applied, andoutputting the multiplexed signal.

A program of the present invention is characterized by making a computerexecute: a processing to receive a wavelength multiplexed opticalsignal; a processing which requests to apply a predetermined change toan optical signal to be output, when the received wavelength multiplexedoptical signal includes an optical signal to which a predeterminedprocessing is applied; and a processing to multiplex a plurality ofoptical signals having different wavelengths including an optical signalto which the predetermined change has been applied, and to output themultiplexed signal.

Advantageous Effects of Invention

The present invention exhibits an effect capable of securing secrecy ofinformation included in the optical signal even when an optical signalis forwarded to a device which is not an original transmissiondestination device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration example of an optical communication system ina first exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of an opticalbranch device 3 in the first exemplary embodiment of the presentinvention.

FIG. 3 is a flow chart illustrating an operational example of theoptical branch device 3 in the first exemplary embodiment of the presentinvention.

FIG. 4 is a diagram illustrating a configuration example of the opticaltransmission/reception device 1-3 in a second exemplary embodiment ofthe present invention.

FIG. 5 is a flow chart illustrating an operational example of theoptical transmission/reception device 1-3 in the second exemplaryembodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration example of the opticalbranch device 3 in a third exemplary embodiment of the presentinvention.

FIG. 7 is a diagram illustrating a state of an optical signal whichtransmits an optical communication system in the third exemplaryembodiment of the present invention.

FIG. 8 is a flow chart illustrating an operational example when theoptical branch device 3 in the third exemplary embodiment of the presentinvention outputs a wavelength multiplexed optical signal to the opticaltransmission/reception device 1-3.

FIG. 9 is a flow chart illustrating an operational example when theoptical branch device 3 in the third exemplary embodiment of the presentinvention outputs a wavelength multiplexed optical signal to an opticalreception device 1-1.

FIG. 10 is a diagram illustrating a configuration example of the opticalbranch device 3 when WSS is used in the third exemplary embodiment ofthe present invention.

FIG. 11 is a diagram illustrating a configuration example of the opticaltransmission/reception device 1-3 in a fourth exemplary embodiment ofthe present invention.

FIG. 12 is a configuration example of a transponder 14 in the fourthexemplary embodiment of the present invention.

FIG. 13 is a flow chart illustrating an operational example of theoptical transmission/reception device 1-3 in the fourth exemplaryembodiment of the present invention.

FIG. 14 is another configuration example of the transponder 14 in thefourth exemplary embodiment of the present invention.

FIG. 15 is a diagram illustrating another configuration example of theoptical transmission/reception device 1-3 in the fourth exemplaryembodiment of the present invention.

FIG. 16 is a diagram illustrating a configuration example of an opticaltransmission device 1-2 in a fifth exemplary embodiment of the presentinvention.

FIG. 17 is a flow chart illustrating an operational example of theoptical transmission device 1-2 in the fifth exemplary embodiment of thepresent invention.

FIG. 18 is a diagram illustrating a configuration example of the opticaltransmission device 1-2 in a sixth exemplary embodiment of the presentinvention.

FIG. 19 is a configuration example of a transponder 124 in the sixthexemplary embodiment of the present invention.

FIG. 20 is a flow chart illustrating an operational example of theoptical transmission device 1-2 in the sixth exemplary embodiment of thepresent invention.

FIG. 21 is another configuration example of the transponder 124 in thesixth exemplary embodiment of the present invention.

FIG. 22 is a configuration example of the optical branch device 3 in aseventh exemplary embodiment of the present invention.

FIG. 23 is a diagram illustrating a configuration example of thetransponder 14 included in the optical transmission/reception device 1-3in the seventh exemplary embodiment of the present invention.

FIG. 24 is a diagram illustrating a configuration example of a variableDGD generator in an eighth exemplary embodiment of the presentinvention.

FIG. 25 is a diagram illustrating another configuration example of avariable DGD generator in the eighth exemplary embodiment of the presentinvention.

FIG. 26 is a configuration example of the optical branch device 3 in theeighth exemplary embodiment of the present invention.

FIG. 27 is a configuration example of the optical branch device 3 in aninth exemplary embodiment of the present invention.

FIG. 28 is a diagram illustrating a configuration example of the opticalbranch device 3 in a tenth exemplary embodiment of the presentinvention.

FIG. 29 is a flow chart illustrating an operational example of theoptical branch device 3 in the tenth exemplary embodiment of the presentinvention.

FIG. 30 is a diagram illustrating a configuration example of the opticalbranch device 3 in an eleventh exemplary embodiment of the presentinvention.

FIG. 31 is a flow chart illustrating an operational example of theoptical branch device 3 in the eleventh exemplary embodiment of thepresent invention.

FIG. 32 is a diagram illustrating a configuration example of acommunication system before a failure occurs in a transmission path 2 ina twelfth exemplary embodiment of the present invention.

FIG. 33 is a table illustrating optical signals transmitted by aninterval between an A base station 10-1 and the optical branch device 3,and an interval between the optical branch device 3 and a B base station10-2, in the communication system of the twelfth exemplary embodiment ofthe present invention.

FIG. 34 is a configuration example of a communication system when afailure occurs in a part of the transmission path 2 and an opticalsignal from a part of the base stations 10 disappears in the twelfthexemplary embodiment of the present invention.

FIG. 35 is a table illustrating a connection relation of the transponder14 which transmits/receives an optical signal in an interval between theA base station 10-1 and the optical branch device 3, and an intervalbetween the optical branch device 3 and the B base station 10-2 of acommunication system in the twelfth exemplary embodiment of the presentinvention.

FIG. 36 is a table illustrating a connection relation of the transponder14 which transmits/receives an optical signal in an interval between theA base station 10-1 and the optical branch device 3, and an intervalbetween the optical branch device 3 and the B base station 10-2 of acommunication system after the optical branch device 3 has switched apath in the twelfth exemplary embodiment of the present invention.

FIG. 37 is a configuration example of an optical communication system ina thirteenth exemplary embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS First Exemplary Embodiment

A summary of the first exemplary embodiment of the present inventionwill be described with reference to the drawings. It is noted that areference sign for each of the drawings in the summary has been addedfor convenience to each element as one example for helpingunderstanding, and the description of the summary should not beconstrued as limiting in any way.

FIG. 1 is a configuration example of an optical communication system inthe first exemplary embodiment of the present invention. As illustratedin FIG. 1, the optical communication system includes an opticalreception device 1-1 which receives a wavelength multiplexed opticalsignal, an optical transmission device 1-2 which transmits a wavelengthmultiplexed optical signal, and an optical transmission/reception device1-3 which transmits/receives a wavelength multiplexed optical signal.The optical communication system illustrated in FIG. 1 includes atransmission path 2 which transmits a wavelength multiplexed opticalsignal, and an optical branch device (Branch Unit: BU) 3 whichmultiplexes and branches a wavelength multiplexed optical signal.

FIG. 2 is a diagram illustrating a configuration example of the opticalbranch device 3. The optical branch device 3 comprises a reception unit30, a demultiplexing unit 32, a processing unit 33, and a multiplexingunit 34.

The reception unit 30 receives a wavelength multiplexed optical signalinput from the transmission path 2.

The optical reception unit 30 may be a branch unit 31. In this case, thebranch unit 31 branches a wavelength multiplexed optical signal inputfrom the transmission path 2, inputs one wavelength multiplexed opticalsignal to the demultiplexing unit 32, and outputs the other wavelengthdemultiplexing signal to another external device (for example, theoptical reception device 1-1). The other wavelength multiplexed opticalsignal is output to another external device (for example, the opticalreception device 1-1) after a predetermined processing is applied inanother device (not illustrated) included in the optical branch device3. The other wavelength multiplexed optical signal is output as it is toanother external device when a predetermined processing does not need tobe applied.

The demultiplexing unit 32 demultiplexes a wavelength multiplexedoptical signal into a first demultiplexed light including a firstwavelength and a second demultiplexed light including a secondwavelength. The demultiplexing unit 32 inputs the first demultiplexedlight to the processing unit 33, and inputs the second demultiplexedlight to the multiplexing unit 34.

The processing unit 33 applies a predetermined processing to the firstdemultiplexed light input from the demultiplexing unit 32, and outputsthe light to the multiplexing unit 34. As the predetermined processing,the processing unit 33 adds a predetermined pattern to an optical signalto be output. The predetermined pattern is, for example, a dummy patternin which 0 and 1 are randomly arranged, or a fixed pattern in which 0and 1 are arranged in a specific pattern. As the predeterminedprocessing, the processing unit 33 may scramble an optical signal to beoutput. As the predetermined processing, the processing unit 33 maydeteriorate transmission characteristics of an optical signal to beoutput.

The multiplexing unit 34 multiplexes the first demultiplexed light onwhich a predetermined processing has been performed input from theprocessing unit 33 and the second demultiplexed light input from thedemultiplexing unit 32, and outputs the multiplexed light to thetransmission path 2.

FIG. 3 is a flow chart illustrating an operational example of theoptical branch device 3 in the first exemplary embodiment of the presentinvention.

The reception unit 30 receives a wavelength multiplexed optical signalinput from the transmission path 2, and inputs the wavelengthmultiplexed optical signal to the demultiplexing unit 32 (S101).

The demultiplexing unit 32 demultiplexes a wavelength multiplexedoptical signal into the first demultiplexed light including the firstwavelength and the second demultiplexed light including the secondwavelength, inputs the first demultiplexed light to the processing unit33, and inputs the second demultiplexed light to the multiplexing unit34 (S102).

The processing unit 33 performs a predetermined processing on the firstdemultiplexed light input from the demultiplexing unit 32, applies apredetermined change thereto, and outputs the light to the multiplexingunit 34 (S103).

The multiplexing unit 34 multiplexes the first demultiplexed light onwhich a predetermined processing has been performed input from theprocessing unit 33 and the second demultiplexed light input from thedemultiplexing unit 32, and outputs the multiplexed light to thetransmission path 2 (S104).

As mentioned above, for example, when an optical signal including datais forwarded to a device which is not an original transmissiondestination, the optical branch device 3 of the first exemplaryembodiment of the present invention performs a predetermined processingon an optical signal including the data. An optical signal on which apredetermined processing has been performed is, for example, an opticalsignal including a predetermined pattern, or a scrambled optical signal,and it is difficult to reproduce data (read data) included in anoriginal optical signal. As a result, even when an optical signalincluding data is forwarded to a device which is not an originaltransmission destination, secrecy of data included in the optical signalcan be secured.

Second Exemplary Embodiment

A second exemplary embodiment of the present invention will be describedwith reference to the drawings. In the second exemplary embodiment ofthe present invention, a description of a configuration similar to thefirst exemplary embodiment of the present invention will be omitted.

A configuration example of an optical communication system in the secondexemplary embodiment of the present invention is similar to the opticalcommunication system illustrated in FIG. 1.

In the second exemplary embodiment of the present invention, awavelength multiplexed optical signal received by the opticaltransmission/reception device 1-3 may include an optical signal to whicha predetermined processing has been applied. The predeterminedprocessing is applied for the purpose that data superimposed on anoptical signal cannot be extracted, and is applied by an opticaltransmission device 1-1 or the optical branch device 3. In other words,the optical transmission device 1-1 or the optical branch device 3applies the predetermined processing to an optical signal which is notdestined for the optical transmission/reception device 1-3, therebysecuring secrecy of data superimposed on the optical signal.

For this reason, it is highly probable that, to a reception unit whichhas received an optical signal to which a predetermined processing isapplied in the optical transmission/reception device 1-3, a channelwhich the optical transmission/reception device 1-3 does not use fortransmitting/receiving data is assigned. It is also highly probablethat, to an output unit (an output unit corresponding to the receptionunit) which outputs an optical signal using the same channel as that ofthe reception unit in the optical transmission/reception device 1-3, achannel which the optical transmission/reception device 1-3 does not usefor transmitting/receiving data is assigned.

Here, when an output unit to which a channel which the opticaltransmission/reception device 1-3 does not use fortransmitting/receiving data is assigned outputs an optical signal onwhich data is superimposed, the optical signal on which data issuperimposed is received by a device which is not an originaldestination. In this case, secrecy of data superimposed on the opticalsignal may not be secured.

Accordingly, the optical transmission/reception device 1-3 of the secondexemplary embodiment of the present invention applies a predeterminedchange to an optical signal output from an output unit corresponding to(whose channel is the same as that of) a reception unit which hasreceived an optical signal to which a predetermined processing has beenapplied. The optical transmission/reception device 1-3 applies apredetermined change to an optical signal from an output unit to which achannel which own device does not use for transmitting/receiving data isassigned such that data cannot be extracted, thereby securing secrecy ofdata superimposed on the optical signal.

FIG. 4 is a diagram illustrating a configuration example of the opticaltransmission/reception device 1-3. The optical transmission/receptiondevice 1-3 comprises a plurality of output units 11-1 to 11-N (whenthere is no particular distinction, referred to as “output unit 11”), amultiplexing unit 12, a control unit 13, a plurality of reception units17-1 to 17-N (when there is no particular distinction, referred to as“reception unit 17”), and a demultiplexing unit 18.

The demultiplexing unit 18 demultiplexes a wavelength multiplexedoptical signal received from the transmission path 2, and outputs thedemultiplexed signals to each of the plurality of reception units 17. Toeach of the plurality of reception units 17, a wavelength of an opticalsignal to be received is assigned. The demultiplexing unit 18 outputs anoptical signal having the assigned wavelength to each of the pluralityof reception units 17.

In the second exemplary embodiment of the present invention, awavelength multiplexed optical signal received by the demultiplexingunit 18 includes an optical signal to which a predetermined processingis applied. The optical signal to which a predetermined processing isapplied is, for example, an optical signal including a predeterminedpattern. The predetermined pattern is a dummy pattern in which 0 and 1are randomly arranged, or a fixed pattern in which 0 and 1 are arrangedin a specific pattern, and data cannot be extracted (read) from anoptical signal including the predetermined pattern. The optical signalto which a predetermined processing is applied may be, for example, ascrambled optical signal or an optical signal whose transmissioncharacteristics are deteriorated, and data cannot be extracted (read)also from such an optical signal.

The output unit 11 outputs an optical signal having a predeterminedwavelength. The output unit 11 includes, for example, a laser or thelike, and can output an optical signal obtained by superimposing data ona light output from the laser. The type of the structure or the like ofthe laser is not restricted, and may be, for example, a variablewavelength laser or the like in which an output wavelength can bechanged.

Among the plurality of output units 11, the control unit 13 specifiesthe reception unit 17 which has received an optical signal to which apredetermined processing is applied, and requests the output unit 11corresponding to the specified reception unit 17 to output an opticalsignal to which a predetermined change has been applied. The output unit11 corresponding to the specified reception unit 17 is the output unit11 which outputs an optical signal by using the same channel as that ofthe reception unit 17.

The control unit 13 watches (monitors) an optical signal received byeach of the plurality of reception units 17, and specifies the receptionunit 17 which has received an optical signal to which a predeterminedprocessing is applied. The control unit 13 may receive a control signalto notify a wavelength of an optical signal to which a predeterminedchange has been applied, and specify the reception unit 17 which hasreceived an optical signal having the wavelength notified by the controlsignal as the reception unit 17 which has received an optical signal towhich a predetermined processing is applied. The control unit 13 mayreceive a notification that an optical signal to which a predeterminedprocessing has been applied is received from at least one of thereception units 17, and specify the notified reception unit 17 as aninput/output unit which has received the optical signal to which apredetermined processing has been applied.

The output unit 11 applies a predetermined change to an optical signalto be output in response to a request from the control unit 13. As thepredetermined change, the output unit 11 adds a predetermined pattern toan optical signal to be output. The predetermined pattern is, forexample, a dummy pattern in which 0 and 1 are randomly arranged, or afixed pattern in which 0 and 1 are arranged in a specific pattern. Asthe predetermined change, the output unit 11 may scramble an opticalsignal to be output. As the predetermined change, the output unit 11 maydeteriorate transmission characteristics of an optical signal to beoutput.

The output unit 11, when not instructed by the control unit 13, convertsan electric signal input from a device (not illustrated in FIG. 2) in aprevious stage into an optical signal, and outputs the optical signal tothe multiplexing unit 12. In other words, the output unit 11 outputs anoptical signal including data when not requested from the control unit13.

The multiplexing unit 12 multiplexes a plurality of optical signalsinput from each of the plurality of output units 11, and outputs themultiplexed signal.

FIG. 5 is a flow chart illustrating an operational example of theoptical transmission/reception device 1-3 in the second exemplaryembodiment of the present invention.

The demultiplexing unit 18 demultiplexes a wavelength multiplexedoptical signal received from the transmission path 2, and outputs thedemultiplexed signals to each of the plurality of reception units 17(S201).

Each of the plurality of reception units 17 receives an optical signalhaving a predetermined wavelength (S202).

Among the plurality of reception units 17, the control unit 13 specifiesthe reception unit 17 which has received an optical signal to which apredetermined processing is applied, and requests the output unit 11corresponding to the specified reception unit 17 to output an opticalsignal to which a predetermined change has been applied (S203).

The output unit 11, when requested from the control unit 13, outputs anoptical signal to be output to which a predetermined change has beenapplied, and, when not requested from the control unit 13, outputs anoptical signal including data to the multiplexing unit 12 (S204).

The multiplexing unit 12 multiplexes a plurality of optical signalsinput from each of the plurality of output units 11, and outputs themultiplexed signal to the transmission path 2 (S205).

As mentioned above, the optical transmission/reception device 1-3 of thesecond exemplary embodiment outputs an optical signal to which apredetermined change has been applied from the output unit 11corresponding to the reception unit 17 which has received an opticalsignal to which a predetermined processing is applied among theplurality of reception units 17.

As mentioned above, in the second exemplary embodiment of the presentinvention, the optical transmission/reception device 1-3 applies apredetermined change to an optical signal output from the output unit 11corresponding to (whose channel is the same as that of) a reception unit17 which has received an optical signal to which a predeterminedprocessing has been applied. For this reason, the opticaltransmission/reception device 1-3 can secure secrecy of datasuperimposed on an optical signal output from the output unit 11 towhich a channel which is not used for transmitting/receiving data isassigned.

Third Exemplary Embodiment

A summary of a third exemplary embodiment of the present invention willbe described with reference to the drawings. In the third exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiments of the presentinvention will be omitted.

A configuration example of an optical communication system in the thirdexemplary embodiment of the present invention is similar to FIG. 1.

FIG. 6 is a diagram illustrating a configuration example of the opticalbranch device 3. The optical branch device 3 comprises a branch unit 31,a demultiplexing unit 32, a processing unit 33, a first multiplexingunit 39, a control unit 35, a first filter 36, a second filter 37, and asecond multiplexing unit 38. The first multiplexing unit 39 correspondsto the multiplexing unit 34 in the first exemplary embodiment of thepresent invention.

The branch unit 31 branches a wavelength multiplexed optical signalinput from the transmission path 2, inputs one wavelength multiplexedoptical signal to the demultiplexing unit 32, and inputs the otherwavelength multiplexed optical signal to the first filter 36.

The control unit 35 notifies the demultiplexing unit 32 of informationabout an optical signal to be input to the processing unit 33. Thecontrol unit 35 may receive a control signal which notifies of awavelength of an optical signal to perform a predetermined processing,and notify the demultiplexing unit 32 of a wavelength of a firstdemultiplexed light which the demultiplexing unit 32 inputs to theprocessing unit 33.

The demultiplexing unit 32 demultiplexes a wavelength multiplexedoptical signal into the first demultiplexed light including the firstwavelength and the second demultiplexed light including the secondwavelength based on the notification from the control unit 35. Thedemultiplexing unit 32 inputs a first demultiplexed light to theprocessing unit 33, and a second demultiplexed light to the firstmultiplexing unit 39.

The processing unit 33 performs a predetermined processing on the firstdemultiplexed light input from the demultiplexing unit 32, and inputsthe light to the first multiplexing unit 39.

The first multiplexing unit 39 multiplexes the first demultiplexed lighton which a predetermined processing has been performed input from theprocessing unit 33 and the second demultiplexed light input from thedemultiplexing unit 32, and outputs the multiplexed light to thetransmission path 2.

Among a plurality of optical signals included in a wavelengthmultiplexed optical signal, the first filter 36 blocks an optical signalwhich is destined for the optical transmission/reception device 1-3, andpasses an optical signal which is destined for the optical receptiondevice 1-1.

Among wavelength multiplexed optical signals from the opticaltransmission/reception device 1-3, the second filter 37 blocks anoptical signal to which a predetermined change has been applied, andpasses the other optical signal.

The second multiplexing unit 38 outputs a wavelength multiplexed opticalsignal obtained by multiplexing an optical signal input from the firstfilter 36 and an optical signal input from the second filter 37 to thetransmission path 2.

FIG. 7 is a diagram illustrating a state of an optical signal whichtransmits an optical communication system in the third exemplaryembodiment of the present invention. FIG. 7 illustrates an example inwhich the processing unit 33 of the optical branch device 3 adds apredetermined pattern to a first demultiplexed light.

An optical transmission device 1-2, as illustrated in FIG. 7, outputs awavelength multiplexed optical signal including an optical signalSub-band 1 (block arrow “1” in FIG. 7) and an optical signal Sub-band 2(block arrow “2” in FIG. 7). In an example of FIG. 7, the optical signalSub-band 1 is an optical signal destined for the optical receptiondevice 1-1, and the optical signal Sub-band 2 is an optical signaldestined for the optical transmission/reception device 1-3.

The branch unit 31 of the optical branch device 3 inputs one wavelengthmultiplexed optical signal output from the optical transmission device1-2, and inputs the other to the first filter 36.

The demultiplexing unit 32 inputs the optical signal Sub-band 1 includedin a wavelength multiplexed optical signal to the processing unit 33,and inputs the optical signal Sub-band 2 to the first multiplexing unit39.

The processing unit 33 outputs an optical signal Sub-band 1′ (blockarrow “predetermined pattern” in FIG. 7) obtained by applying apredetermined processing to the input optical signal Sub-band 1. Theprocessing unit 33 adds, for example, a predetermined pattern as apredetermined processing to the optical signal Sub-band 1. Since theoptical signal Sub-band 1 is an optical signal destined for the opticalreception device 1-1, the optical branch device 3 outputs an opticalsignal (i.e., optical signal Sub-band 1′) obtained by applying apredetermined processing to the optical signal Sub-band 1 so as not tobe received by the optical transmission/reception device 1-3.

The first multiplexing unit 39 outputs a wavelength multiplexed opticalsignal obtained by multiplexing the optical signal Sub-band 2 input fromthe demultiplexing unit 32 and the optical signal Sub-band 1′ input fromthe processing unit 33 to the optical transmission/reception device 1-3.

The optical transmission/reception device 1-3 outputs a wavelengthmultiplexed optical signal obtained by multiplexing an optical signalSub-band 3 (block arrow “3” in FIG. 7) destined for the opticalreception device 1-1 and an optical signal (block arrow “predeterminedpattern” in FIG. 7) obtained by applying a predetermined change to anoptical signal whose wavelength corresponds to the optical signalSub-band 1′. The optical transmission/reception device 1-3 adds, forexample, a predetermined pattern as a predetermined change to theoptical signal Sub-band 1.

Among wavelength multiplexed optical signals input from the opticaltransmission/reception device 1-3, the second filter 37 passes only theoptical signal Sub-band 3 destined for the optical reception device 1-1,and blocks an optical signal to which a predetermined change has beenapplied.

On the other hand, among the input wavelength multiplexed opticalsignals, the first filter 36 passes only the optical signal Sub-band 1destined for the optical reception device 1-1, and blocks the opticalsignal Sub-band 2.

The second multiplexing unit 38 outputs a wavelength multiplexed opticalsignal obtained by multiplexing the optical signal Sub-band 1 input fromthe first filter and the optical signal Sub-band 3 input from the secondfilter to the optical reception device 1-1.

FIG. 8 and FIG. 9 are flow charts illustrating an operational example ofthe optical branch device 3 in the third exemplary embodiment of thepresent invention. FIG. 8 is a flow chart illustrating an operationalexample when the optical branch device 3 outputs a wavelengthmultiplexed optical signal to the optical transmission/reception device1-3.

The branch unit 31 branches a wavelength multiplexed optical signalinput from the transmission path 2, inputs one signal to demultiplexingunit 32, and inputs the other signal to the first filter 36 (S301).

The control unit 35 notifies a wavelength of an optical signal to beinput to the processing unit 33 to the demultiplexing unit 32 (S302).

The demultiplexing unit 32 demultiplexes a wavelength multiplexedoptical signal into the first demultiplexed light including the firstwavelength and the second demultiplexed light including the secondwavelength based on the notification from the control unit 35, inputs afirst demultiplexed light to the processing unit 33, and a seconddemultiplexed light to the first multiplexing unit 39 (S303).

The processing unit 33 performs a predetermined processing on the firstdemultiplexed light input from the demultiplexing unit 32, and outputsthe light to the first multiplexing unit 39 (S304).

The first multiplexing unit 39 multiplexes the first demultiplexed lighton which a predetermined processing has been performed input from theprocessing unit 33 and the second demultiplexed light input from thedemultiplexing unit 32, and outputs the multiplexed light to thetransmission path 2 (S305).

FIG. 9 is a flow chart illustrating an operational example when theoptical branch device 3 outputs a wavelength multiplexed optical signalto the optical reception device 1-1.

The branch unit 31 branches a wavelength multiplexed optical signalinput from the transmission path 2, inputs one wavelength multiplexedoptical signal to the demultiplexing unit 32, and inputs the otherwavelength multiplexed optical signal to the first filter 36 (S401).

Among a plurality of optical signals included in a wavelengthmultiplexed optical signal, the first filter 36 blocks an optical signalwhich is destined for the optical transmission/reception device 1-3, andpasses an optical signal which is destined for the optical receptiondevice 1-1 (S402).

The second filter 37 passes an optical signal other than an opticalsignal to which a predetermined change has been applied included in awavelength multiplexed optical signal from the opticaltransmission/reception device 1-3 (S403).

The second multiplexing unit 38 outputs a wavelength multiplexed opticalsignal obtained by multiplexing an optical signal input from the firstfilter 36 and an optical signal input from the second filter 37 to thetransmission path 2 (S404).

The demultiplexing unit 32 may be a 3-port wavelength filter module.Among a wavelength multiplexed optical signal input from the first port,the 3-port wavelength filter module, including three ports, for example,reflects an optical signal Sub-band 1 and passes an optical signalSub-band 2 from the second port. The 3-port wavelength filter moduleoutputs the reflected optical signal Sub-band 1 from the third port.Accordingly, by connecting the second port of the 3-port wavelengthfilter module to the first multiplexing unit 39 and connecting the thirdport to the processing unit 33, only the optical signal Sub-band 1 canbe input to the processing unit 33. The 3-port wavelength filter moduleis a variable filter which can change an optical signal which reflectsor passes based on an instruction from the control unit 35.

In the optical branch device 3, the demultiplexing unit 32 may be a WSS(Wavelength Selective Switch). In the optical branch device 3, in placeof the first filter 36, the second filter 37, and the secondmultiplexing unit 38, a WSS may be employed.

A WSS is a switch which can independently set any path for each of aplurality of wavelengths included in a wavelength multiplexed opticalsignal. Here, as the WSS, a WSS described in Japanese Patent No. 5128254can be used. The WSS includes a multiplexing/demultiplexing function,and can independently demultiplex or multiplex each of a plurality ofoptical signals included in a wavelength multiplexed optical signal.

FIG. 10 is a diagram illustrating a configuration example of the opticalbranch device 3 when a WSS is used. As illustrated in FIG. 10, theoptical branch device 3 comprises a first WSS 40 in place of thedemultiplexing unit 32. The first WSS 40 inputs at least one opticalsignal included in a wavelength multiplexed optical signal based on anotification from the control unit 35, and inputs the other opticalsignal (an optical signal which is not input to the processing unit 33)to the first multiplexing unit 39.

As illustrated in FIG. 10, the optical branch device 3 comprises asecond WSS 41 in place of the first filter 36, the second filter 37, andthe second multiplexing unit 38. The second WSS 41 multiplexes anoptical signal destined for the optical reception device 1-1 among aplurality of optical signals included in a wavelength multiplexedoptical signal from the optical transmission device 1-2 and an opticalsignal destined for the optical reception device 1-1 among a pluralityof optical signals included in a wavelength multiplexed optical signalfrom the optical transmission/reception device 1-3. The second WSS 41blocks an optical signal destined for the optical transmission/receptiondevice 1-3 among a plurality of optical signals included in a wavelengthmultiplexed optical signal from the optical transmission device 1-2. Thesecond WSS blocks an optical signal to which a predetermined change hasbeen applied among a plurality of optical signals included in awavelength multiplexed optical signal from the opticaltransmission/reception device 1-3.

As mentioned above, the optical branch device 3 in the third exemplaryembodiment of the present invention performs a predetermined processingon the optical signal in such a way that, for example, an optical signaldestined for the optical reception device 1-1 is not forwarded to theoptical transmission/reception device 1-3. As a result, the opticalbranch device 3 can secure secrecy of data included in the opticalsignal even when an optical signal destined for the optical receptiondevice 1-1 is forwarded to the optical transmission/reception device1-3.

Fourth Exemplary Embodiment

A summary of a fourth exemplary embodiment of the present invention willbe described with reference to the drawings. In the fourth exemplaryembodiment of the present invention, a description of a configurationsimilar to the first exemplary embodiment of the present invention andthe second exemplary embodiment of the present invention will beomitted.

A configuration example of an optical communication system in the fourthexemplary embodiment of the present invention is similar to FIG. 1.

FIG. 11 is a diagram illustrating a configuration example of the opticaltransmission/reception device 1-3. The optical transmission/receptiondevice 1-3 comprises a multiplexing unit 12, a control unit 13, aplurality of transponders 14-1 to 14-N (when there is no particular needfor distinction, referred to as “transponder 14”), a plurality ofreception units 17-1 to 17-N, and a demultiplexing unit 18. In thefourth exemplary embodiment of the present invention, the transponder 14corresponds to the output unit 11 in the second exemplary embodiment ofthe present invention.

Among the plurality of transponders 14, the control unit 13 specifiesthe reception unit 17 which has received an optical signal to which apredetermined processing is applied, and requests the transponder 14corresponding to the specified reception unit 17 to output an opticalsignal to which a predetermined change has been applied.

Each of the transponders 14 outputs an optical signal of a predeterminedwavelength.

FIG. 12 is a configuration example of the transponder 14 in the fourthexemplary embodiment of the present invention. The transponder 14comprises a client module 141, a Framer LSI 142, a processing unit 143,and a line module 144. LSI is an abbreviation of large scale integration(large scale integrated circuit).

The client module 141 converts an optical signal received from a clientdevice (not illustrated) into an electric signal, and outputs theelectric signal as a signal received from a client to the Framer LSI142.

The Framer LSI 142 accommodates the client signal input from the clientmodule 141 in a frame for a line signal, and outputs the signal to theprocessing unit 143.

The processing unit 143 outputs an electric signal including apredetermined pattern (such as a dummy pattern or a fixed pattern) inplace of the frame for a line signal to the line module 144 in responseto a request from the control unit 13. On the other hand, when a controlsignal which requests to output an optical signal of a predeterminedpattern is not received, the frame for a line signal received from theFramer LSI 142 is output to the line module 144.

The processing unit 143, in response to a request from the control unit13, may as a scrambler randomly reshuffle a bit string of an electricsignal input from the Framer LSI 142.

The line module 144 converts the input electric signal (a frame for aline signal or an electric signal of a predetermined pattern) into anoptical signal of a predetermined wavelength, and outputs the signal tothe multiplexing unit 12.

FIG. 13 is a flow chart illustrating an operational example of theoptical transmission/reception device 1-3 in the fourth exemplaryembodiment of the present invention. FIG. 13 is an example when theoptical transmission/reception device 1-3 transmits an optical signal.

The client module 141 converts an optical signal received from a clientdevice (not illustrated) into an electric signal, and outputs theelectric signal as a signal received from a client to the Framer LSI 142(S501).

The Framer LSI 142 accommodates the client signal input from the clientmodule 141 in a frame for a line signal, and outputs the signal to theprocessing unit 143 (S502).

The processing unit 143 determines whether the control unit 13 hasrequested to output an optical signal to which a predetermined changehas been applied (S503).

The processing unit 143, in response to a request from the control unit13 (YES in S503), applies a predetermined change to the received linesignal frame, and outputs the frame to the line module 144 (S504).

On the other hand, the processing unit 143, when not requested from thecontrol unit 13 (NO in S503), outputs the received line signal frame asit is to the line module 144 (S505).

The line module 144 converts the frame for a line signal input from theprocessing unit 143 into an optical signal, and outputs the opticalsignal to the multiplexing unit 12 (S506).

The multiplexing unit 12 outputs a wavelength multiplexed optical signalobtained by multiplexing a plurality of optical signals input from theplurality of transponders 14 to the transmission path 2 (S507).

The transponder 14 may be a configuration example illustrated in FIG.14. In this case, the processing unit 143, in response to a request fromthe control unit 13, outputs an electric signal including apredetermined pattern (such as a dummy pattern or a fixed pattern) tothe line module 144. The line module 144, when an electric signalincluding a predetermined pattern is input from the processing unit 143,converts, in place of the frame for a line signal, an electric signalincluding a predetermined pattern into an optical signal of apredetermined wavelength, and outputs the signal to the multiplexingunit 12.

The optical transmission/reception device 1-3 may be a configurationexample illustrated in FIG. 15. As illustrated in FIG. 15, the opticaltransmission/reception device 1-3 comprises a transponder 14, a controlunit 13, and an optical multiplexing/demultiplexing unit 19.

The optical multiplexing/demultiplexing unit 19 demultiplexes awavelength multiplexed optical signal received from the transmissionpath 2, and outputs the demultiplexed signals to each of the pluralityof transponders 14. To each of the plurality of transponders 14, awavelength of an optical signal to be input/output is assigned. Theoptical multiplexing/demultiplexing unit 19 outputs an optical signalhaving the assigned wavelength to each of the plurality of transponders14. The optical multiplexing/demultiplexing unit 19 multiplexes aplurality of optical signals input from each of the plurality oftransponders 14, and outputs the multiplexed signal. In the fourthexemplary embodiment of the present invention, a wavelength multiplexedoptical signal received by the optical multiplexing/demultiplexing unit19 includes an optical signal to which a predetermined processing hasbeen applied.

In an example of FIG. 15, a case in which the transponder 14 of theoptical transmission/reception device 1-3 has received an optical signalfrom the optical multiplexing/demultiplexing unit 19 will be described.

The line module 144 converts an optical signal received from themultiplexing unit 12 into an electric signal, and outputs the signal asa line-received signal (line signal frame) to the processing unit 143.The processing unit 143 outputs the line-received signal (frame for aline signal) input from the line module 144 to the Framer LSI 142.

The Framer LSI 142 extracts a client signal from the frame for a linesignal input from the processing unit 143, and outputs the extractedsignal as an electric signal to the client module 141.

The client module 141 converts the electric signal input from the FramerLSI 42 into an optical signal, and transmits the converted signal as aclient signal to a client device (not illustrated).

In the optical transmission/reception device 1-3 illustrated in FIG. 15,a configuration and an operation when the transponder 14 of the opticaltransmission/reception device 1-3 transmits an optical signal to theoptical multiplexing/demultiplexing unit 19 are similar to the case ofFIG. 11 described above.

As mentioned above, in the fourth exemplary embodiment of the presentinvention, the optical transmission/reception device 1-3 applies apredetermined change to an optical signal output from the transponder 14corresponding to (whose channel is the same as that of) a reception unit17 which has received an optical signal to which a predeterminedprocessing has been applied. For this reason, the opticaltransmission/reception device 1-3 can secure secrecy of datasuperimposed on an optical signal output from the transponder 14 towhich a channel which is not used for transmitting/receiving data isassigned.

Fifth Exemplary Embodiment

A summary of a fifth exemplary embodiment of the present invention willbe described with reference to the drawings.

In the fifth exemplary embodiment of the present invention, an opticaltransmission device 1-2 outputs an optical signal to which apredetermined change has been applied based on a predetermined condition(for example, an optical signal output from the transmission unit 121has been forwarded to a device which is not an original transmissiondestination).

In the fifth exemplary embodiment of the present invention, aconfiguration example of an optical communication system is similar to aconfiguration example of an optical communication system illustrated inFIG. 1.

FIG. 16 is a diagram illustrating a configuration example of the opticaltransmission device 1-2. The optical transmission device 1-2 comprises atransmission unit 121, a multiplexing unit 122, and a control unit 123.The optical transmission device 1-2 comprises a plurality oftransmission units 121.

The multiplexing unit 122 outputs a wavelength multiplexed signal lightobtained by multiplexing optical signals input from each of theplurality of transmission units 121 to the transmission path 2.

The control unit 123, when a predetermined condition is satisfied,requests the transmission unit 121 to apply a predetermined change to anoptical signal to be output.

The predetermined condition is, for example, that a control signal whichrequests to output an optical signal of a predetermined pattern has beenreceived. The control signal is transmitted to the control unit 123 whena failure occurs in the transmission path 2 and when an optical signaloutput from the optical transmission device 1-2 is forwarded to a devicewhich is not an original transmission destination.

The transmission unit 121, when instructed from the control unit 123,applies a predetermined change to an optical signal to be output, andoutputs the signal to the multiplexing unit 122. The optical signal towhich a predetermined change has been applied is, for example, anoptical signal including a predetermined pattern. The predeterminedpattern is, for example, a dummy pattern in which 0 and 1 are randomlyarranged, or a fixed pattern in which 0 and 1 are arranged in a specificpattern.

The transmission unit 121, when not instructed by the control unit 123,converts an electric signal input from a device (not illustrated in FIG.16) in a previous stage into an optical signal, and outputs the opticalsignal to the multiplexing unit 122. In other words, the transmissionunit 121 outputs an optical signal including data when not instructed bythe control unit 123.

FIG. 17 is a flow chart illustrating an operational example of theoptical transmission device 1-2 in the fifth exemplary embodiment of thepresent invention.

The control unit 123, when a predetermined condition is satisfied,requests the transmission unit 121 to apply a predetermined change to anoptical signal to be output (S601).

The transmission unit 121 determines whether the control unit 123 hasinstructed (S602).

The transmission unit 121, when instructed from the control unit 123(YES in S602), outputs an optical signal to which a predetermined changehas been applied to the multiplexing unit 122 (S603).

The transmission unit 121, when not instructed by the control unit 123(NO in S602), converts the input electric signal into an optical signal,and outputs the signal to the multiplexing unit 122 (S604).

The multiplexing unit 122 outputs a wavelength multiplexed signal lightobtained by multiplexing a plurality of optical signals input from aplurality of transmission units 121 to the transmission path 2 (S605).

As mentioned above, the optical transmission device 1-2 of the fifthexemplary embodiment of the present invention outputs an optical signalto which a predetermined change has been applied based on apredetermined condition (for example, an optical signal output from thetransmission unit 121 has been forwarded to a device which is not anoriginal transmission destination). An optical signal to which apredetermined change has been applied is, for example, an optical signalincluding a dummy pattern in which 0 and 1 are randomly arranged, or afixed pattern in which 0 and 1 are arranged in a specific pattern, andit is difficult to reproduce an original optical signal. As a result,the optical transmission device 1-2 can secure secrecy of data includedin the optical signal even when an optical signal including data isforwarded to a device which is not an original transmission destination.

Sixth Exemplary Embodiment of the Present Invention

A summary of a sixth exemplary embodiment of the present invention willbe described with reference to the drawings. In the sixth exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiments of the presentinvention will be omitted.

A configuration example of an optical communication system in the sixthexemplary embodiment of the present invention is similar to FIG. 1.

FIG. 18 is a diagram illustrating a configuration example of the opticaltransmission device 1-2. The optical transmission device 1-2 comprises amultiplexing unit 122, a control unit 123, and a plurality oftransponders 124-1 to 124-N (when there is no particular need fordistinction, referred to as “transponder 124”). The transponder 124 inthe sixth exemplary embodiment of the present invention corresponds tothe transmission unit 121 in the fifth exemplary embodiment of thepresent invention.

The control unit 123, when a predetermined condition is satisfied,instructs the transponder 124 to output an optical signal including apredetermined pattern.

The predetermined condition is, for example, that a control signal whichrequests to output an optical signal of a predetermined pattern has beenreceived. The control signal is transmitted to the control unit 123 whena failure occurs in the transmission path 2 and when an optical signaloutput from the optical transmission device 1-2 is forwarded to a devicewhich is not an original transmission destination.

The transponder 124, when instructed from the control unit 123, outputsan optical signal of a predetermined pattern to the multiplexing unit122.

The transponder 124, when not instructed by control unit 123, convertsan electric signal input from a device in a previous stage (for example,a client device) into an optical signal, and outputs the signal to themultiplexing unit 122.

FIG. 19 is a configuration example of the transponder 124 in the sixthexemplary embodiment of the present invention. The transponder 124comprises a client module 241, a Framer LSI 242, a processing unit 243,and a line module 244.

The client module 241 converts an optical signal received from a clientdevice (not illustrated) into an electric signal, and outputs the signalas a signal received from a client to the Framer LSI 242.

The Framer LSI 242 accommodates the client signal input from the clientmodule 241 in a frame for a line signal, and outputs the signal to theprocessing unit 243.

The processing unit 243, when a control signal which requests to outputa signal of a predetermined pattern is received, outputs an electricsignal including a predetermined pattern (such as a dummy pattern or afixed pattern) in place of the frame for a line signal to the linemodule 244. On the other hand, when a control signal which requests tooutput an optical signal of a predetermined pattern is not received, theframe for a line signal received from the Framer LSI 242 is output tothe line module 244.

The processing unit 243, in place of generation of a dummy pattern and afixed pattern, may as a scrambler randomly reshuffle a bit string of anelectric signal input from the Framer LSI 242.

The line module 244 converts the input electric signal (a frame for aline signal or an electric signal of a predetermined pattern) into anoptical signal of a predetermined wavelength, and outputs the signal tothe multiplexing unit 122.

FIG. 20 is a flow chart illustrating an operational example of theoptical transmission device 1-2 in the sixth exemplary embodiment of thepresent invention.

The client module 241 converts an optical signal received from a clientdevice (not illustrated) into an electric signal, and outputs theelectric signal as a signal received from a client to the Framer LSI 242(S701).

The Framer LSI 242 accommodates the client signal input from the clientmodule 241 in a frame for a line signal, and outputs the signal to theprocessing unit 243 (S702).

The control unit 123, when a predetermined condition is satisfied,instructs the processing unit 243 in the transponder 124 to output anoptical signal including a predetermined pattern (S703).

The processing unit 243 determines whether the control unit 123 hasinstructed (S704).

The processing unit 243, when instructed from the control unit 123 (YESin S704), outputs an optical signal of a predetermined pattern (S705).

On the other hand, the processing unit 243, when not instructed by thecontrol unit 123 (NO in S704), converts a frame for a line signal inputfrom the Framer LSI 242 into an optical signal, and outputs the signalto the multiplexing unit 122 (S706).

The multiplexing unit 122 outputs a wavelength multiplexed signal lightobtained by multiplexing a plurality of optical signals input from theplurality of transponders 124 to the transmission path 2 (S707).

The transponder 124 may be a configuration example illustrated in FIG.21. In this case, the processing unit 243, when a control signal whichrequests to output a signal of a predetermined pattern is received,outputs an electric signal including a predetermined pattern (such as adummy pattern or a fixed pattern) to the line module 244. The linemodule 244, when an electric signal including a predetermined pattern isinput from the processing unit 243, converts, in place of the frame fora line signal, an electric signal including a predetermined pattern intoan optical signal of a predetermined wavelength, and outputs the signalto the multiplexing unit 122.

As mentioned above, the optical transmission device 1-2 of the sixthexemplary embodiment of the present invention, when a control signalwhich requests to output an optical signal of a predetermined pattern isreceived, outputs an optical signal of a predetermined pattern (such asa dummy pattern or a fixed pattern). For this reason, the opticaltransmission device 1-2 can transmit a signal of a predetermined patternin place of an optical signal including data, for example, when anoptical signal including data has been forwarded to a device which isnot an original transmission destination. As a result, the opticaltransmission device 1-2 can prevent an optical signal including datafrom being forwarded to a device which is not an original transmissiondestination, thereby securing secrecy of data included in the opticalsignal.

Seventh Exemplary Embodiment

A summary of a seventh exemplary embodiment of the present inventionwill be described with reference to the drawings. In the seventhexemplary embodiment of the present invention, a description of aconfiguration similar to the above-described exemplary embodiments ofthe present invention will be omitted.

The seventh exemplary embodiment of the present invention is anexemplary embodiment when a processing unit is a polarization scrambler.In other words, the seventh exemplary embodiment of the presentinvention is an exemplary embodiment when the processing unit 33 of theoptical branch device 3 is a polarization scrambler 42 of FIG. 22described below, and the processing unit 143 of the opticaltransmission/reception device 1-3 is a polarization scrambler 145 ofFIG. 23 described below. The processing unit 243 of the opticaltransmission device 1-1 may also be a polarization scrambler.

In the seventh exemplary embodiment of the present invention, data issuperimposed on an optical signal by polarization modulation.

Here, the polarization scramblers 42 and 145 polarization-modulate theinput optical signal, and output the polarization-modulated opticalsignal.

For the polarization scramblers 42 and 145, a polarization scramblerdescribed, for example, in Japanese Patent No. 3777045 can be used. Thepolarization scrambler is obtained by forming an optical waveguide on asubstrate having an electrooptic effect such as lithium niobate,providing an electrode on the substrate, and optically coupling anoptical fiber to an input/output portion of the optical waveguide. In apolarization scrambler having such a configuration, a signal light of alinearly polarized wave enters the optical waveguide with itspolarization direction inclined at 45 degrees with respect to thevertical direction of the optical waveguide, whereby the linearlypolarized wave is decomposed into a vertical component and a horizontalcomponent. At this time, by applying a modulating signal such as a sinewave to an electrode provided on the optical waveguide, the refractiveindices of the vertical component and the horizontal component of theoptical waveguide change by an electrooptic effect, thereby changing thevelocity of each direction component of propagation in the opticalwaveguide. By this, a phase difference is generated between the verticalcomponent and the horizontal component of a signal light, which makesthe polarization state of an optical signal to be emitted random.

As mentioned above, in the seventh exemplary embodiment of the presentinvention, data is superimposed on an optical signal by a polarizationmodulation. For this reason, when the polarization state of an opticalsignal is made random by the polarization scramblers 42 or 145, datacannot be decoded from the optical signal. As a result, since datacannot be restored even when the optical signal is forwarded to a devicewhich is not an original transmission destination, secrecy of the datais secured.

A configuration example of an optical communication system in theseventh exemplary embodiment of the present invention is similar to FIG.1.

FIG. 22 is a configuration example of the optical branch device 3 in theseventh exemplary embodiment of the present invention. As illustrated inFIG. 22, the optical branch device 3 includes the polarization scrambler42 in place of the processing unit 33. The polarization scrambler 42polarization-modulates an optical signal input from the demultiplexingunit 32, and inputs the polarization-modulated optical signal to a firstmultiplexing unit 39.

A configuration example of the optical transmission/reception device 1-3in the seventh exemplary embodiment of the present invention is similarto FIG. 11.

FIG. 23 is a diagram illustrating a configuration example of thetransponder 14 included in the optical transmission/reception device 1-3in the seventh exemplary embodiment of the present invention. Thetransponder 14 includes a polarization scrambler 145. The polarizationscrambler 145 polarization-modulates an optical signal input from theline module 144 based on a control signal from the control unit 13. Inthis case, the control unit 13, when a control signal which requests tooutput an optical signal of a predetermined pattern is received,requests the polarization scrambler 145 to polarization-modulates anoptical signal.

As mentioned above, the optical branch device 3 in the seventh exemplaryembodiment of the present invention polarization-modulates apredetermined optical signal included in a wavelength multiplexedoptical signal to be transmitted to the optical transmission/receptiondevice 1-3. For example, the optical branch device 3polarization-modulates an optical signal destined for the opticalreception device 1-1 by the polarization scrambler 42, thereby makingthe optical signal irreproducible even when the optical signal isreceived by the optical transmission/reception device 1-3. As describedabove, the optical branch device 3 in the seventh exemplary embodimentof the present invention can make the optical signal irreproducible evenwhen an optical signal including data is forwarded to a device which isnot an original transmission destination, thereby securing secrecy ofdata included in the optical signal.

The optical transmission/reception device 1-3 of the seventh exemplaryembodiment outputs an optical signal to which a polarization modulationhas been applied from the transponder 14 corresponding to the receptionunit 17 which has received an optical signal to which a predeterminedprocessing is applied among a plurality of transponders 14. As a result,the optical transmission/reception device 1-3 can use an optical signaloutput from at least one of the plurality of transponders as a dummylight, and can secure secrecy of data which has been superimposed on theoptical signal.

Further, when the processing unit 243 is a polarization scrambler, theoptical transmission device 1-2 can apply a polarization modulation toan optical signal including data and transmit the data, for example,when an optical signal including data is forwarded to a device which isnot an original transmission destination. As a result, the opticaltransmission device 1-2 can make the optical signal irreproducible evenwhen an optical signal including data is forwarded to a device which isnot an original transmission destination, thereby securing secrecy ofdata included in the optical signal.

Eighth Exemplary Embodiment

A summary of an eighth exemplary embodiment of the present inventionwill be described with reference to the drawings. In the eighthexemplary embodiment of the present invention, a description of aconfiguration similar to the above-described exemplary embodiments willbe omitted.

The eighth exemplary embodiment of the present invention is an exemplaryembodiment when the processing unit 33 of the optical branch device 3 isa PMD (Polarization Mode Dispersion) addition device 43 of FIG. 26described below. In the eighth exemplary embodiment of the presentinvention, the PMD addition device 43 generates a primary PMD and asecondary PMD with respect to an optical signal to be input, therebymaking an optical signal output from the PMD addition device 43irreproducible from the input optical signal.

An optical signal to which a PMD is added splits into polarized waveshaving different oscillating directions by 90 degrees to propagate. Thesplit two polarized waves propagate at different velocities to cause adifference in time at which the waves reach the optical reception device1-1. Such a difference is referred to as a DGD (Differential GroupDelay), which is a scale for indicating the degree of a PMD. Since, as aDGD of an optical signal increases, adjacent data in time overlap, adigital data of “0” and “1” superimposed on the optical signal cannot becorrectly distinguished. In other words, the PMD addition device 43purposely generates a PMD causing a large DGD with respect to an opticalsignal, thereby making data superimposed on the optical signalirreproducible.

Here, for the PMD addition device 43, a variable DGD generator describedin Japanese Patent No. 4142300 can be used. FIG. 24 is a diagramillustrating a configuration example of a variable DGD generatordescribed in Japanese Patent No. 4142300. The variable DGD generatorcomprises a collimator 431, a birefringent medium 432, a variablefaraday rotator 433, and a reflection mirror 434.

An optical signal is converted into a light beam in the collimator 431,and enters the birefringent medium 432. The propagation velocities ofpolarized wave components in the directions of the fast axis and theslow axis of the birefringent medium 432 of the light beam which hasentered the birefringent medium 432 differ. In other words, a DGD isadded to a light beam which has entered the birefringent medium 432.

A light beam to which a DGD has been added enters the variable faradayrotator 433, rotated at a predetermined rotation angle (θ/2), and isemitted from the variable faraday rotator 433. The optical signalemitted from the variable faraday rotator 433 is reflected by thereflection mirror 434, and reenters the variable faraday rotator 433. Aplane of polarization of the light beam which has reentered the variablefaraday rotator 433 is further rotated by a rotation angle of θ/2, andthe light beam is emitted from the variable faraday rotator 433. A DGDis added to the light beam whose plane of polarization has been rotatedby θ, and the light beam is converted into an optical signal in thecollimator 431. As described above, since an optical path is turned backby the reflection mirror 434, a DGD is added twice. In other words, thevariable DGD generator generates a primary PMD and a secondary PMD withrespect to an optical signal.

In the PMD addition device 43, the properties of the birefringent medium432 or the rotation angle θ of the variable faraday rotator 433 is setin such a way that a PMD can be generated to a degree to which the inputoptical signal cannot be reproduced from an optical signal to be output.

For the birefringent medium 432, for example, an electrooptic crystalsuch as lithium niobate or lanthanum lead titanate zirconate can beused. As illustrated in FIG. 25, the variable DGD generator may beconfigured by arranging the collimator 431, the birefringent medium 432,and the variable faraday rotator 433 in series without using thereflection mirror 434.

FIG. 26 is a configuration example of the optical branch device 3 in theeighth exemplary embodiment of the present invention. As illustrated inFIG. 26, the optical branch device 3 includes the PMD addition device 43in place of the processing unit 33. The PMD addition device 43 generatesa PMD in an optical signal input from the demultiplexing unit 32, andinputs the optical signal to the first multiplexing unit 39.

The optical branch device 3 in the eighth exemplary embodiment of thepresent invention passes, for example, an optical signal destined forthe optical reception device 1-1, among optical signals included in awavelength multiplexed optical signal to be transmitted to the opticaltransmission/reception device 1-3, to the PMD addition device 43, andgenerates a PMD with respect to the optical signal. As a result, theoptical transmission/reception device 1-3 which has received an opticalsignal to which the PMD has been added cannot extract data superimposedon the optical signal. As a result, the optical branch device 3 in theeighth exemplary embodiment can make the optical signal irreproducibleeven when an optical signal including data is forwarded to a devicewhich is not an original transmission destination, thereby securingsecrecy of data included in the optical signal.

Ninth Exemplary Embodiment

A summary of a ninth exemplary embodiment of the present invention willbe described with reference to the drawings. In the ninth exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiments of the presentinvention will be omitted.

The ninth exemplary embodiment of the present invention is an exemplaryembodiment when the processing unit 33 of the optical branch device 3 isa highly nonlinear fibers (HNLF: Highly Nonlinear Fibers) 44 of FIG. 27described below.

Here, for a highly nonlinear fibers 44, for example, a non-lineardispersion-shifting optical fiber of Japanese Patent No. 4070083 can beused. The non-linear dispersion-shifting optical fiber adds a nonlinearoptics phenomenon to an input optical signal, thereby generating a phasemodulation, a wavelength conversion, or the like. Examples of anonlinear optics phenomenon in the non-linear dispersion-shiftingoptical fiber include four-wave mixing, self-phase modulation, crossphase modulation, and stimulated Brillouin scattering. When such aphenomenon is caused in the non-linear dispersion-shifting opticalfiber, a wavelength conversion, phase modulation, scattering or the likeoccurs in the input optical signal, and a noise component in the opticalsignal increases, or the input optical signal cannot be sufficientlytransmitted. For this reason, as the degree of wavelength conversion,phase modulation, scattering or the like generated in an optical signalincreases, a receiving side device cannot reproduce information (data)superimposed on the input optical signal.

As mentioned above, the ninth exemplary embodiment of the presentinvention inputs an optical signal to the highly nonlinear fibers 44 togenerate wavelength conversion, phase modulation, scattering or the likein the optical signal, thereby making data superimposed on the opticalsignal irreproducible.

A configuration example of an optical communication system in the ninthexemplary embodiment of the present invention is similar to FIG. 1.

FIG. 27 is a configuration example of the optical branch device 3 in theninth exemplary embodiment of the present invention. As illustrated inFIG. 27, the optical branch device 3 includes the highly nonlinearfibers 44 in place of the processing unit 33. The waveform of an opticalsignal input from the demultiplexing unit 32 deteriorates while theoptical signal transmits through the highly nonlinear fibers 44. Thehighly nonlinear fibers 44 input an optical signal whose waveform isdeteriorated to the first multiplexing unit 39. In the ninth exemplaryembodiment of the present invention, the length and properties of thehighly nonlinear fibers 44 are set (adjusted) in such a way that thewaveform of the input optical signal can be deteriorated to a degree tobe irreproducible from an optical signal to be output.

The optical branch device 3 in the ninth exemplary embodiment of thepresent invention passes, for example, an optical signal destined forthe optical reception device 1-1 through the highly nonlinear fibers 44,thereby making the optical signal irreproducible in the opticaltransmission/reception device 1-3. As a result, the optical branchdevice 3 in the ninth exemplary embodiment of the present invention canmake the optical signal irreproducible even when an optical signalincluding data is forwarded to a device which is not an originaltransmission destination, thereby securing secrecy of data included inthe optical signal.

Tenth Exemplary Embodiment

A summary of a tenth exemplary embodiment of the present invention willbe described with reference to the drawings. In the tenth exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiments will be omitted.

In the tenth exemplary embodiment of the present invention, a variablefilter is arranged in the optical branch device 3 illustrated in FIG. 6in place of the demultiplexing unit 32, and the control unit 35specifies a wavelength of an optical signal which passes through thevariable filter. The control unit 35 instructs the processing unit 33 tooutput an optical signal having a wavelength corresponding to thewavelength of an optical signal to be blocked by the variable filter andhaving a predetermined pattern. The wavelength corresponding to thewavelength of an optical signal is, for example, the same wavelength asthat of the optical signal.

FIG. 28 is a diagram illustrating a configuration example of the opticalbranch device 3 in the tenth exemplary embodiment of the presentinvention. The optical branch device 3 comprises a variable filter 45 inplace of the demultiplexing unit 32.

The variable filter 45 passes only an optical signal having apredetermined wavelength among wavelength multiplexed optical signalsinput from the branch unit 31 based on an instruction from the controlunit 35. The variable filter 45 inputs an optical signal which haspassed therethrough to the first multiplexing unit 39.

The control unit 35, for example, notifies a wavelength of an opticalsignal to pass among wavelength multiplexed optical signals based on acontrol signal. On the other hand, the control unit 35 specifies to theprocessing unit 33 a wavelength of an optical signal to be output. Thewavelength of an optical signal to be output from the processing unit 33is a wavelength corresponding to the wavelength of an optical signalblocked by the variable filter 45.

The processing unit 33 outputs an optical signal to which apredetermined processing has been applied to the first multiplexing unit39.

The first multiplexing unit 39 outputs a wavelength multiplexed opticalsignal obtained by multiplexing an optical signal input from thevariable filter 45 and an optical signal to which a predeterminedprocessing has been applied input from the processing unit 33 to theoptical transmission/reception device 1-3.

FIG. 29 is a flow chart illustrating an operational example of theoptical branch device 3 in the tenth exemplary embodiment of the presentinvention. FIG. 29 is an operational example when the optical branchdevice 3 outputs a wavelength multiplexed optical signal including anoptical signal to which a predetermined processing has been applied.

The branch unit 31 branches a wavelength multiplexed optical signalinput from the transmission path 2, inputs one wavelength multiplexedoptical signal to the variable filter 45, and inputs the other to thefirst filter 36 (S801).

To the variable filter 45, the control unit 35 specifies a wavelength ofan optical signal to pass, and specifies a wavelength of an opticalsignal to output to the processing unit 33 (S802).

The variable filter 45 passes only an optical signal having apredetermined wavelength among wavelength multiplexed optical signalsinput from the branch unit 31 based on an instruction from the controlunit 35, and inputs the signal to the first multiplexing unit 39 (S803).

The processing unit 33 outputs an optical signal which has a wavelengthcorresponding to the wavelength specified by the control unit 35 and towhich a predetermined processing has been applied (S804).

The first multiplexing unit 39 outputs a wavelength multiplexed opticalsignal obtained by multiplexing an optical signal input from thevariable filter 45 and an optical signal to which a predeterminedprocessing has been applied input from the processing unit 33 to thetransmission path 2 (S805).

As mentioned above, the optical branch device 3 in the tenth exemplaryembodiment of the present invention outputs the optical signal to whicha predetermined processing has been applied in such a way that, forexample, an original optical signal cannot be restored even when anoptical signal destined for the optical reception device 1-1 isforwarded to the optical transmission/reception device 1-3. As a result,the optical branch device 3 can make a device which is not an originaltransmission destination not reproduce an optical signal including data,thereby securing secrecy of data included in the optical signal.

Eleventh Exemplary Embodiment

A summary of an eleventh exemplary embodiment of the present inventionwill be described with reference to the drawings. In the eleventhexemplary embodiment of the present invention, a description of aconfiguration similar to the above-described exemplary embodiments ofthe present invention will be omitted.

FIG. 30 is a diagram illustrating a configuration example of the opticalbranch device 3 in the eleventh exemplary embodiment of the presentinvention. The optical branch device 3 comprises a first filter 36, afirst branch unit 46, and a third filter 47. The first branch unit 46branches a wavelength multiplexed optical signal from the opticaltransmission device 1-2, inputs one to the third filter 47, and inputsthe other to the first filter 36. The third filter 47 passes only anoptical signal of an optical signal Sub-band 2 destined for the opticaltransmission/reception device 1-3 among wavelength multiplexed opticalsignals. On the other hand, first filter 36 passes only an opticalsignal of an optical signal destined for the optical reception device1-1 Sub-band 1 among wavelength multiplexed optical signals.

The optical branch device 3 comprises a processing unit 33, a controlunit 35, a second filter 37, a second multiplexing unit 38, a firstmultiplexing unit 39, and a second branch unit 48. The second branchunit 48 inputs an optical signal (Sub-band 1) input from the firstfilter 36 to the processing unit 33 and the second multiplexing unit 38.

The control unit 35 notifies a wavelength of an optical signal to passto the first filter 36 and the third filter 47. The control unit 35 mayreceive a control signal for requesting replacement to an optical signalof a predetermined pattern, and specify a wavelength of an opticalsignal which passes through each of the first filter 36 and the thirdfilter 47 based on the received control signal.

The processing unit 33 outputs an optical signal which has a wavelengthcorresponding to a wavelength of an optical signal to be output from thefirst filter 36 and to which a predetermined processing has been appliedto the first multiplexing unit 39. The first multiplexing unit 39outputs a wavelength multiplexed optical signal obtained by multiplexingan optical signal input from the third filter 47 and an optical signalto which a predetermined processing has been applied input from theprocessing unit 33 to the transmission path 2.

The second filter 37 passes an optical signal other than an opticalsignal to which a predetermined change has been applied included in awavelength multiplexed optical signal from the opticaltransmission/reception device 1-3. The second multiplexing unit 38outputs a wavelength multiplexed optical signal obtained by multiplexingan optical signal input from the second branch unit 48 and an opticalsignal input from the second filter 37 to the transmission path 2.

FIG. 31 is a flow chart illustrating an operational example of theoptical branch device 3 in the eleventh exemplary embodiment of thepresent invention. FIG. 31 is an operational example when the opticalbranch device 3 outputs a wavelength multiplexed optical signalincluding an optical signal to which a predetermined processing isapplied.

The first branch unit 46 branches a wavelength multiplexed opticalsignal input from the transmission path 2, inputs one wavelengthmultiplexed optical signal to the third filter 47, and inputs the otherto the first filter 36 (S901).

The control unit 35 specifies a wavelength of an optical signal to passto the first filter 36 and the third filter 47 (S902).

The third filter 47 passes only an optical signal having a predeterminedwavelength among wavelength multiplexed optical signals input from thefirst branch unit 46 based on an instruction from the control unit 35,and inputs the signal to the first multiplexing unit 39 (S903).

The first filter 36 passes only an optical signal having a predeterminedwavelength among wavelength multiplexed optical signals input from thefirst branch unit 46 based on an instruction from the control unit 35,and inputs the signal to the second branch unit 48 (S904).

The second branch unit 48 inputs an optical signal input from the firstfilter 36 to the processing unit 33 and the second multiplexing unit 38(S905).

The processing unit 33 outputs an optical signal obtained by applying apredetermined processing to a light input from the second branch unit 48(S906).

The first multiplexing unit 39 outputs a wavelength multiplexed opticalsignal obtained by multiplexing an optical signal input from the thirdfilter 47 and an optical signal of a predetermined pattern input fromthe processing unit 33 to the transmission path 2 (S907).

As mentioned above, the optical branch device 3 in the eleventhexemplary embodiment of the present invention outputs the optical signalto which a predetermined processing has been applied in such a way that,for example, an original optical signal cannot be restored even when anoptical signal destined for the optical reception device 1-1 isforwarded to the optical transmission/reception device 1-3. As a result,the optical branch device 3 can make a device which is not an originaltransmission destination of an optical signal including data notreproduce an optical signal including data, thereby securing secrecy ofdata included in the optical signal.

Twelfth Exemplary Embodiment

A twelfth exemplary embodiment of the present invention will bedescribed with reference to the drawings. In the twelfth exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiments will be omitted.

In the twelfth exemplary embodiment of the present invention, when afailure is generated in a part of the transmission path 2 and an opticalsignal from a part of base stations disappears, a path is switched inthe BU (optical branch device) 3 to compensate the disappeared opticalsignal by an optical signal from another base station. In this case, theoptical transmission device 1-2 outputs an optical signal which is to betransmitted to a device which is not an original communicationcounterpart by converting the signal into an optical signal to which apredetermined change has been applied in advance to prevent the devicewhich is not an original communication counterpart from receiving theoptical signal used for the compensation.

The total power of an optical signal propagating in the transmissionpath 2 is set to be constant. When a part of wavelength components ofthe optical signal disappears by a breakage of the transmission path 2or the like, the total power of the optical signal is kept constant byamplifying another wavelength component of the optical signal.

By increasing only the power of a specific wavelength component of anoptical signal up to a predetermined value or larger, however, opticalspectrum changes caused by deterioration of a waveform of the opticalsignal or the like by a nonlinear effect of an optical fiber, therebydeteriorating the transmission quality of the optical signal.

Accordingly, in the twelfth exemplary embodiment of the presentinvention, when an optical signal from a part of base stations isblocked and a part of wavelength components of an optical signal whichis carried in the transmission path 2 disappears, the disappearedwavelength component is compensated by an optical signal from anotherbase station. This prevents only the power of a specific wavelengthcomponent of an optical signal from increasing, thereby inhibitingdeterioration of the transmission quality of the optical signal.

The optical signal used for compensation is, however, forwarded to adevice which is not an original communication counterpart. Accordingly,in the twelfth exemplary embodiment of the present invention, thetransponder 14 of the optical transmission device 1-2 converts anoptical signal to be forwarded to a device which is not an originalcommunication counterpart into an optical signal to which a change isapplied in advance, and transmits the converted signal. As a result, anoptical signal used for the compensation is not received by a devicewhich is not an original transmission destination. In other words, inthe twelfth exemplary embodiment of the present invention, a disappearedpart of wavelength components of an optical signal propagating in thetransmission path 2 can be compensated, and at the same time, anoriginal optical signal is made irreproducible even when an opticalsignal used for compensation is received by a device which is not anoriginal communication counterpart.

FIG. 32 is a diagram illustrating a configuration example of acommunication system before a failure occurs in the transmission path 2in the twelfth exemplary embodiment of the present invention. Asillustrated in FIG. 32, the communication system includes the A basestation 10-1, the B base station 10-2, a C base station 10-3, a D basestation 10-4, and the optical branch device 3 to which these basestations are connected. Each base station 10 includes the transponder14, a client device 15, and wavelength multiplexing units 16-1 to 16-4.In FIG. 32, the client devices 15 are described as devices 15-1-A to15-5-A, devices 15-1-B to 15-5-B, devices 15-1-C to 15-3-C, devices15-1-D to 15-3-D. Similarly, the transponders 14 are also described inFIG. 32 distinguished by reference signs.

FIG. 33 is a table illustrating optical signals transmitted by aninterval between an A base station 10-1 and the optical branch device 3and an interval between the optical branch device 3 and a B base station10-2 in the communication system illustrated in FIG. 32. Since a failurehas not occurred in the transmission path 2, in both of an intervalbetween the A base station 10-1 and the optical branch device 3 and aninterval between the optical branch device 3 and the B base station10-2, five pairs of the transponders 14 perform communication.

On the other hand, FIG. 34 is a configuration example of a communicationsystem when a failure occurs in a part of the transmission path 2 and anoptical signal from a part of the base stations 10 disappears in thetwelfth exemplary embodiment of the present invention.

An example of a communication system of FIG. 34 is, for example, anexample in which a failure has occurred in the transmission paths 2-2and 2-3 between the C base station 10-3 and the D base station 10-4 andthe optical branch device 3, and an optical signal from the C basestation and the D base station to the optical branch device 3 hasdisappeared. Specifically, among optical signals transmitted in aninterval between the A base station 10-1 and the optical branch device3, and an interval between the optical branch device 3 and the B basestation 10-2, a wavelength component of an optical signal which has beentransmitted/received between the A base station 10-1 and the C basestation 10-3, and between the B base station 10-2 and the D base station10-4 disappears.

FIG. 35 is a table illustrating a connection relation of the transponder14 which transmits/receives an optical signal in an interval between theA base station 10-1 and the optical branch device 3 and an intervalbetween the optical branch device 3 and the B base station 10-2 of thecommunication system illustrated in FIG. 34. As described above, when afailure occurs in the transmission path 2 between the C base station andthe D base station, and the optical branch device 3, a connectionbetween the A base station 10-1 and the C base station 10-3, and aconnection between the B base station 10-2 and the D base station 10-4break. As a result, as illustrated in FIG. 35, in an interval betweenthe A base station 10-1 and the optical branch device 3 and an intervalbetween the optical branch device 3 and the B base station 10-2, only acommunication between the A base station 10-1 and the B base station10-2 survives.

When an optical signal is continued to be transmitted in the states ofFIG. 34 and FIG. 35 (in a state in which a part of wavelength componentsdisappears in a wavelength multiplexed optical signal), however, thetransmission quality of an optical signal deteriorates as describedabove. Accordingly, in the twelfth exemplary embodiment of the presentinvention, the optical branch device 3 switches a path to compensate thedisappeared optical signal by an optical signal from another basestation.

In the twelfth exemplary embodiment of the present invention, theoptical branch device 3 switches a path in such a way that an opticalsignal transmitted from the transponders 14-3-A, 14-4-A, and 14-5-A ofthe A base station 10-1 is received by the transponders 14-3-B, 14-4-B,and 14-5-B of the B base station 10-2.

FIG. 36 is a table illustrating a connection relation of the transponder14 which transmits/receives an optical signal in an interval between theA base station 10-1 and the optical branch device 3 and an intervalbetween the optical branch device 3 and the B base station 10-2 of acommunication system after the optical branch device 3 has switched apath. When the optical branch device 3 switches a path, an opticalsignal transmitted/received between the transponder 14 of the A basestation 10-1 and the transponder 14 of the C base station 10-3 isforwarded to the transponder 14 of the B base station 10-2, and adisappeared optical signal is compensated. An optical signaltransmitted/received between the transponder 14 of the B base station10-1 and the transponder 14 of the D base station 10-4 is forwarded tothe transponder 14 of the A base station 10-1, and a disappeared opticalsignal is compensated.

An optical signal used for compensation is, however, forwarded to adevice (i.e., the transponder 14 of the B base station 10-2 or thetransponder 14 of the A base station 10-1) which is not an originalcommunication counterpart.

Accordingly, in the twelfth exemplary embodiment of the presentinvention, an optical signal used for compensation may be an opticalsignal to which a predetermined processing has been applied by theoptical branch device 3. Examples of the predetermined change includegenerating a primary PMD and a secondary PMD to an optical signal to beinput or polarization modulation of an optical signal to be output. Inother words, the demultiplexing unit 32 of the optical branch device 3inputs an optical signal (for example, an optical signal output from thetransponder 14-3-A of the A base station 10-1) used for compensation tothe processing unit 33, and outputs the signal in place of an opticalsignal to which a predetermined change has been applied. By outputtingan optical signal to which a predetermined change has been applied, thetransponder 14-3-B of the B base station 10-2 cannot reproduce anoriginal optical signal even when an optical signal including data(i.e., an optical signal output from the transponder 14-3-A of the Abase station 10-1) is received.

In the twelfth exemplary embodiment of the present invention, thetransponder 14 in the optical transmission device 1-2 may output anoptical signal to which a predetermined change has been applied in placeof an optical signal including data. For example, an optical signaltransmitted from the transponder 14-3-A of the A base station 10-1 isused for compensation, and is received by the transponder 14-3-B of theB base station 10-2. A device of an original communication counterpartof the transponder 14-3-B of the B base station 10-2 is a transponder14-1-D of the D base station 10-4. In this case, the transponder 14-3-Aof the A base station 10-1 outputs an optical signal to which apredetermined change has been applied in place of an optical signal(optical signal to be forwarded to a device which is not a device of anoriginal communication counterpart) used for compensation. By outputtingan optical signal to which a predetermined change has been applied, thetransponder 14-3-B of the B base station 10-2 cannot reproduce anoriginal optical signal even when the optical signal is received.

In the twelfth exemplary embodiment of the present invention, asmentioned above, when a failure is generated in the transmission path 2and an optical signal from a part of base stations disappears, a path inthe optical branch device 3 is switched to compensate the disappearedoptical signal by an optical signal from anther base station. Thisprevents only the power of a specific wavelength component of an opticalsignal from increasing, thereby inhibiting deterioration of thetransmission quality of the optical signal. In this case, an opticalsignal used by the optical branch device 3 for compensation is anoptical signal to which a predetermined processing has been applied. Asa result, a device which is not a device of an original communicationcounterpart cannot reproduce an original optical signal even when anoptical signal including data is received. As a result, the opticalbranch device 3 can prevent a device which is not an originaltransmission destination from receiving an optical signal includingdata, thereby securing secrecy of data included in the optical signal.

In the twelfth exemplary embodiment of the present invention, thetransponder 14 on the transmitting side converts an optical signal usedfor compensation, which is an optical signal including data, into anoptical signal to which a predetermined change has been applied. As aresult, a device which is not a device of an original communicationcounterpart cannot reproduce an original optical signal even when theoptical signal is received. As a result, the optical transmission device1-2 can prevent a device which is not an original transmissiondestination from receiving an optical signal including data, therebysecuring secrecy of data included in the optical signal.

Thirteenth Exemplary Embodiment

A thirteenth exemplary embodiment of the present invention will bedescribed with reference to the drawings. In the thirteenth exemplaryembodiment of the present invention, a description of a configurationsimilar to the above-described exemplary embodiment will be omitted.

FIG. 37 is a configuration example of an optical communication system inthe thirteenth exemplary embodiment of the present invention. Asillustrated in FIG. 37, the optical communication system includes theoptical reception device 1-1, the optical transmission device 1-2, theoptical transmission/reception device 1-3, the transmission path 2, theoptical branch device 3, and an EMS (Element Management System) 4. Theconfigurations of the optical reception device 1-1, the opticaltransmission device 1-2, the optical transmission/reception device 1-3,the transmission path 2 and the optical branch device 3 are similar tothose of the optical reception device 1-1, the optical transmissiondevice 1-2, the optical transmission/reception device 1-3, thetransmission path 2, and the optical branch device 3 of theabove-described exemplary embodiments.

The EMS 4 is a device which performs network management of an opticalcommunication system, and collects information about a communicationpath of an optical signal from a device included in the opticalcommunication system. The EMS 4 detects a failure which has occurred inthe transmission path 2 based on the information about a communicationpath, and requests the optical branch device 3 to switch a path. The EMS4 requests to switch a path in such a way that an optical signaltransmitted from the transponders 14-3-A, 14-4-A and 14-5-A of the Abase station 10-1 is received by the transponders 14-3-B, 14-4-B, and14-5-B of the B base station 10-2 when a failure occurs in thetransmission path 2 between the C base station and the D base stationand the optical branch device 3, as illustrated in FIG. 34.

When a path of the optical branch device 3 is switched, in order to makean optical signal to be used for compensation an optical signal to whicha predetermined change has been applied, the EMS 4 instructs thedemultiplexing unit 32 in the optical branch device 3 to input theoptical signal to be used for compensation to the processing unit 33.When a failure occurs in the transmission path 2 between the C basestation and the D base station, and the optical branch device, asillustrated in FIG. 34, the EMS 4 requests demultiplexing unit 32 toconvert an optical signal output from the transponders 14-3-A, 14-4-A,and 14-5-A of the A base station 10-1 into an optical signal to which apredetermined change has been applied. This prevents the B base stationfrom receiving an optical signal output from the transponders 14-3-A,14-4-A and 14-5-A of the A base station 10-1.

The demultiplexing unit 32 requested from the EMS 4 inputs an opticalsignal to be used for compensation to the processing unit 33 based onthe request.

When a predetermined processing is applied to an optical signal having apredetermined wavelength in the optical branch device 3, the EMS maynotify the predetermined wavelength to the opticaltransmission/reception device 1-3. When the notification is received,the optical transmission/reception device 1-3 can apply a predeterminedchange to an optical signal output from the output unit 11 (transponder14) which receives an optical signal having the notified predeterminedwavelength.

The EMS 4, when a failure occurred in the transmission path 2 isdetected, requests the processing unit 33 of the transponder 14 includedin the optical transmission device 1-2 to add a predetermined processingto an optical signal. The EMS 4, when a failure occurs in thetransmission path 2 between the C base station and the D base stationand the optical branch device as illustrated in FIG. 34, requests theprocessing unit 33 of the transponders 14-3-A, 14-4-A and 14-5-A of theA base station 10-1 to add a predetermined processing to an opticalsignal.

In response to a request from the EMS 4, the processing unit 33requested from the EMS 4 outputs, in place of the input electric signal,an electric signal including a dummy pattern in which 0 and 1 arerandomly arranged, or a fixed pattern in which 0 and 1 are arranged in aspecific pattern, or an electric signal in which a bit string israndomly reshuffled.

As mentioned above, in the thirteenth exemplary embodiment of thepresent invention, the EMS 4 instructs the demultiplexing unit 32 of theoptical branch device 3 to input an optical signal used for compensationto the processing unit 33. As a result, the optical branch device 3 canprevent an optical signal including data from being forwarded to adevice which is not an original transmission destination, therebysecuring secrecy of data included in the optical signal.

The EMS 4 performs network management, and requests the optical branchdevice 3 to switch a path or requests the optical transmission device1-2 to add a predetermined processing to an optical signal and transmitthe signal. As a result, the optical transmission device 1-2 can preventan optical signal including data from being forwarded to a device whichis not an original transmission destination while keeping the power ofan optical signal transmitted in the transmission path 2 constant,thereby securing secrecy of data included in the optical signal.

Fourteenth Exemplary Embodiment

A fourteenth exemplary embodiment of the present invention will bedescribed. In the fourteenth exemplary embodiment, a computer, a CPU(Central Processing Unit), an MPU (Micro-Processing Unit), or the likeof the optical transmission device 1-2, the optical branch device 3, orthe optical transmission/reception device 1-3 executes a software(program) which realizes a function of each of the above-describedexemplary embodiments. In the fourteenth exemplary embodiment of thepresent invention, a device which executes the software (program) is notlimited to the optical transmission device 1-2, the optical branchdevice 3, or the optical transmission/reception device 1-3, and anydevice can be employed.

In the fourteenth exemplary embodiment of the present invention, theoptical transmission device 1-2, the optical branch device 3, or theoptical transmission/reception device 1-3 acquires a software (program)which realizes a function of each of the above-described exemplaryembodiments via various storage media such as a CD-R (Compact DiscRecordable) or via a network. A program which the optical transmissiondevice 1-2, the optical branch device 3, or the opticaltransmission/reception device 1-3 acquires, or a storage medium storingthe program constitutes the present invention. The software (program)may be stored, for example, in a predetermined storage unit included inthe optical transmission device 1-2, the optical branch device 3 or theoptical transmission/reception device 1-3.

A computer, a CPU, an MPU, or the like of the optical transmissiondevice 1-2, the optical branch device 3, or the opticaltransmission/reception device 1-3 reads a program code of the acquiredsoftware (program), and executes the program code. As a result, the sameprocessing as the processing of the optical transmission device 1-2, theoptical branch device 3 or the optical transmission/reception device 1-3in each of the above-described exemplary embodiments is executed.

The fourteenth exemplary embodiment of the present invention can beapplied to uses such as a program realized in a computer, a CPU, an MPU,or the like of the optical transmission device 1-2, the optical branchdevice 3, or the optical transmission/reception device 1-3.

Although exemplary embodiments of the present invention have beendescribed, the present invention is not limited to the above-describedexemplary embodiments. The present invention can be carried out based onvariations, substitutions, or adjustment of each exemplary embodiment.The present invention can also be carried out in any combination of theexemplary embodiments. In other words, the present invention involvesvarious variations or modifications which can be realized in accordancewith all the content of the disclosure and technical ideas herein.

This application claims priority based on Japanese Patent ApplicationNo. 2014-066137 filed on Mar. 27, 2014, the entire disclosure of whichis herein incorporated.

A part or the whole of the above-described exemplary embodiments mayalso be described as the following supplementary notes, but the presentinvention is not limited thereto.

[Supplementary Note 1]

An optical transmission/reception device comprising:

a demultiplexing unit which receives a wavelength multiplexed opticalsignal, and demultiplexes the signal into a plurality of opticalsignals;

a plurality of reception units which receive each of the plurality ofoptical signals demultiplexed by the demultiplexing unit;

a plurality of output units which respectively output optical signalshaving different wavelengths;

a control unit which requests to apply a predetermined change to anoptical signal output from at least one of the plurality of output unitswhen the received wavelength multiplexed optical signal includes anoptical signal to which a predetermined processing is applied; and

a multiplexing unit which multiplexes the plurality of optical signalsoutput from the plurality of output units and outputs the multiplexedsignal.

[Supplementary Note 2]

The optical transmission/reception device according to supplementarynote 1, wherein the control unit requests to apply the predeterminedchange to an optical signal output from an output unit corresponding toa reception unit which has received the optical signal to which apredetermined processing is applied.

[Supplementary Note 3]

The optical transmission/reception device according to supplementarynote 1 or 2, wherein each of the plurality of output units, whenrequested from the control unit, adds a predetermined pattern to theoptical signal to be output as the predetermined change.

[Supplementary Note 4]

The optical transmission/reception device according to any one ofsupplementary notes 1 to 3, wherein each of the plurality of outputunits, when requested from the control unit, scrambles the opticalsignal to be output as the predetermined change.

[Supplementary Note 5]

The optical transmission/reception device according to any one ofsupplementary notes 1 to 4, wherein each of the plurality of outputunits, when requested from the control unit, deteriorates transmissioncharacteristics of the optical signal to be output as the predeterminedchange.

[Supplementary Note 6]

The optical transmission/reception device according to any one ofsupplementary notes 1 to 5, wherein each of the plurality of outputunits comprises a processing unit which applies a predetermined changeto the optical signal to be output when requested from the control unit.

[Supplementary Note 7]

An optical communication system comprising:

an optical communication device which outputs a wavelength multiplexedoptical signal; and

an optical transmission/reception device comprising:

-   -   a demultiplexing unit which receives the wavelength multiplexed        optical signal, and demultiplexes the signal into a plurality of        optical signals;    -   a plurality of reception units which receive each of the        plurality of optical signals demultiplexed by the demultiplexing        unit;    -   a plurality of output units which respectively output optical        signals having different wavelengths;    -   a control unit which requests to apply a predetermined change to        an optical signal output from at least one of the plurality of        output units when the received wavelength multiplexed optical        signal includes an optical signal to which a predetermined        processing is applied; and    -   a multiplexing unit which multiplexes the plurality of optical        signals output from the plurality of output units and outputs        the multiplexed signal.

[Supplementary Note 8]

The optical communication system according to supplementary note 7,wherein the optical communication device adds the predeterminedprocessing to an optical signal other than an optical signal destinedfor the optical transmission/reception device among optical signalsincluded in the wavelength multiplexed optical signal.

[Supplementary Note 9]

The optical communication system according to supplementary note 7 or 8,further comprising

a control device which notifies a wavelength of an optical signal towhich the optical communication device has applied the predeterminedprocessing to the optical transmission/reception device,

wherein the control unit requests an output unit which outputs anoptical signal having a wavelength notified by the control device toapply a predetermined change to the optical signal to be output.

[Supplementary Note 10]

An optical communication method comprising:

receiving a wavelength multiplexed optical signal,

requesting to apply a predetermined change to an optical signal to beoutput when the received wavelength multiplexed optical signal includesan optical signal to which a predetermined processing is applied,multiplexing a plurality of optical signals having different wavelengthsincluding an optical signal to which the predetermined change has beenapplied, and outputting the multiplexed signal.

[Supplementary Note 11]

The optical communication method according to supplementary note 10, themethod comprising adding a predetermined pattern to the optical signalto be output in response to the request.

[Supplementary Note 12]

The optical communication method according to supplementary note 10 or11, the method comprising scrambling the optical signal to be output inresponse to the request.

[Supplementary Note 13]

The optical communication method according to any one of supplementarynotes 10 to 12, the method comprising deteriorating transmissioncharacteristics of the optical signal to be output in response to therequest.

[Supplementary Note 14]

A program which allows a computer to execute:

a processing to receive a wavelength multiplexed optical signal;

a processing to request to apply a predetermined change to an opticalsignal to be output when the received wavelength multiplexed opticalsignal includes an optical signal to which a predetermined processing isapplied; and

a processing to multiplex a plurality of optical signals havingdifferent wavelengths including the optical signal to which apredetermined change has been applied, and to output.

[Supplementary Note 15]

The program according to supplementary note 14, comprising a processingto add a predetermined pattern to the optical signal to be output inresponse to the request.

[Supplementary Note 16]

The program according to supplementary note 14 or 15, comprising aprocessing to scramble the optical signal to be output in response tothe request.

[Supplementary Note 17]

The program according to any one of supplementary notes 14 to 16,comprising a processing to deteriorate transmission characteristics ofthe optical signal to be output in response to the request.

REFERENCE SIGNS LIST

-   -   1-1 optical reception device    -   1-2 optical transmission device    -   1-3 optical transmission/reception device    -   2, 2-1, 2-2, 2-3 transmission path    -   3 optical branch device    -   4 EMS    -   11, 11-1, 11-N output unit    -   12 multiplexing unit    -   13 control unit    -   14, 14-1, 14-N transponder    -   15, 15-1, 15-N client device    -   16, 16-1, 16-N wavelength multiplexing unit    -   17 reception unit    -   18 demultiplexing unit    -   19 optical multiplexing/demultiplexing unit    -   30 reception unit    -   31 branch unit    -   32 demultiplexing unit    -   33 processing unit    -   34 multiplexing unit    -   35 control unit    -   36 first filter    -   37 second filter    -   38 second multiplexing unit    -   39 first multiplexing unit    -   40 first WSS    -   41 second WSS    -   42 polarization scrambler    -   43 PMD addition device    -   44 highly nonlinear fibers    -   45 variable filter    -   46 first branch unit    -   47 third filter    -   48 second branch unit    -   121 transmission unit    -   122 multiplexing unit    -   123 control unit    -   124, 124-1, 124-N transponder    -   141 client module    -   142 Framer LSI    -   143 processing unit    -   144 line module    -   145 polarization scrambler    -   241 client module    -   242 Framer LSI    -   243 processing unit    -   244 line module    -   431, 431-1, 431-2 collimator    -   432, 432-1, 432-2, 432-3 birefringent medium    -   433, 433-1, 433-2 variable faraday rotator    -   434 reflection mirror

The invention claimed is:
 1. An optical transmission device comprising:a transponder configured to output an optical signal; and a multiplexerconfigured to output a multiplexed optical signal including the opticalsignal to a transmission path, wherein the transponder is furtherconfigured to, in response to a failure in the transmission path, applya process to the optical signal.
 2. The optical transmission deviceaccording to claim 1, further comprising: a controller configured tosend a processing request to the transponder, wherein the controller isfurther configured to: receive a control signal in response to thefailure in the transmission path, and send the processing request afterreceiving the control signal, and the transponder is further configuredto, in response to the processing request from the controller, apply theprocess to the optical signal.
 3. The optical transmission deviceaccording to claim 1, further comprising: a controller configured tosend a processing request to the transponder, wherein the controller isfurther configured to: receive a control signal in response to switchinga destination of the optical signal, and send the processing requestafter receiving the control signal, and the transponder is furtherconfigured to, in response to the processing request from thecontroller, apply the process to the optical signal.
 4. The opticaltransmission device according to claim 1, wherein, in response to thefailure in the transmission path, the transponder is further configuredto add a predetermined pattern to the optical signal.
 5. The opticaltransmission device according to claim 1, wherein, in response to thefailure in the transmission path, the transponder is further configuredto scramble the optical signal.
 6. The optical transmission deviceaccording to claim 1, wherein, in response to the failure in thetransmission path, the transponder is further configured to degradeoptical properties of the optical signal.
 7. An optical communicationsystem comprising: an optical transmission device configured to output amultiplexed optical signal; and an optical reception device configuredto receive the multiplexed optical signal, wherein the opticaltransmission device comprises: a transponder configured to output anoptical signal; and a multiplexer configured to output the multiplexedoptical signal including the optical signal to a transmission path,wherein the transponder is further configured to, in response to afailure in the transmission path, apply a process to the optical signal.8. The optical communication system according to claim 7, furthercomprising: a controller configured to send a processing request to thetransponder, wherein the controller is further configured to: receive acontrol signal in response to the failure in the transmission path; andsend the processing request after receiving the control signal, and thetransponder is further configured to, in response to the processingrequest from the controller, apply the process to the optical signal. 9.The optical communication system according to claim 7, furthercomprising: a controller configured to send a processing request to thetransponder, wherein the controller is further configured to: receive acontrol signal in response to switching a destination of the opticalsignal; and send the processing request after receiving the controlsignal, and the transponder is further configured to, in response to theprocessing request from the controller, apply the process to the opticalsignal.
 10. The optical communication system according to claim 7,wherein, in response to the failure in the transmission path, thetransponder is further configured to add a predetermined pattern to theoptical signal.
 11. The optical communication system according to claim7, wherein, in response to the failure in the transmission path, thetransponder is further configured to scramble the optical signal. 12.The optical communication system according to claim 7, wherein, inresponse to the failure in the transmission path, the transponder isfurther configured to degrade optical properties of the optical signal.13. An optical communication method performed inside an opticaltransmission device, the optical communication method comprising:generating an optical signal; applying a process to the optical signalin response to a failure in a transmission path; outputting amultiplexed optical signal including the optical signal to thetransmission path; receiving a control signal in response to switching adestination of the optical signal; sending a processing request afterreceiving the control signal; and applying the process to the opticalsignal in response to the processing request.
 14. The opticalcommunication method according to claim 13, further comprising, inresponse to the failure in the transmission path, adding a predeterminedpattern to the optical signal.
 15. The optical communication methodaccording to claim 13, further comprising, in response to the failure inthe transmission path, scrambling the optical signal.
 16. The opticalcommunication method according to claim 13, further comprising, inresponse to the failure in the transmission path, degrading opticalproperties of the optical signal.